Longer Integration Times Research Articles

Time-Resolved Dynamic Optical Coherence Tomography for Retinal Blood Flow Analysis.

Optical coherence tomography (OCT) representations in clinical practice are static and do not allow for a dynamic visualization and quantification of blood flow. This study aims to present a method to analyze retinal blood flow dynamics using time-resolved structural OCT. We developed novel imaging protocols to acquire video-rate time-resolved OCT B-scans (1024 × 496 pixels, 10 degrees field of view) at four different sensor integration times (integration time of 44.8 µs at a nominal A-scan rate of 20 kHz, 22.4 µs at 40 kHz, 11.2 µs at 85 kHz, and 7.24 µs at 125 kHz). The vessel centers were manually annotated for each B-scan and surrounding subvolumes were extracted. We used a velocity model based on signal-to-noise ratio (SNR) drops due to fringe washout to calculate blood flow velocity profiles in vessels within five optic disc diameters of the optic disc rim. Time-resolved dynamic structural OCT revealed pulsatile SNR changes in the analyzed vessels and allowed the calculation of potential blood flow velocities at all integration times. Fringe washout was stronger in acquisitions with longer integration times; however, the ratio of the average SNR to the peak SNR inside the vessel was similar across all integration times. We demonstrated the feasibility of estimating blood flow profiles based on fringe washout analysis, showing pulsatile dynamics in vessels close to the optic nerve head using structural OCT. Time-resolved dynamic OCT has the potential to uncover valuable blood flow information in clinical settings.

Atmospheric Limitations for High-frequency Ground-based Very Long Baseline Interferometry

Very long baseline interferometry (VLBI) provides the highest-resolution images in astronomy. The sharpest resolution is nominally achieved at the highest frequencies, but as the observing frequency increases, so too does the atmospheric contribution to the system noise, degrading the sensitivity of the array and hampering detection. In this paper, we explore the limits of high-frequency VLBI observations using ngehtsim, a new tool for generating realistic synthetic data. ngehtsim uses detailed historical atmospheric models to simulate observing conditions, and it employs heuristic visibility detection criteria that emulate single- and multifrequency VLBI calibration strategies. We demonstrate the fidelity of ngehtsim’s predictions using a comparison with existing 230 GHz data taken by the Event Horizon Telescope (EHT), and we simulate the expected performance of EHT observations at 345 GHz. Though the EHT achieves a nearly 100% detection rate at 230 GHz, our simulations indicate that it should expect substantially poorer performance at 345 GHz; in particular, observations of M87* at 345 GHz are predicted to achieve detection rates of ≲20% that may preclude imaging. Increasing the array sensitivity through wider bandwidths and/or longer integration times—as enabled through, e.g., the simultaneous multifrequency upgrades envisioned for the next-generation EHT—can improve the 345 GHz prospects and yield detection levels that are comparable to those at 230 GHz. M87* and Sgr A* observations carried out in the atmospheric window around 460 GHz could expect to regularly achieve multiple detections on long baselines, but analogous observations at 690 and 875 GHz consistently obtain almost no detections at all.

Radio Emission From a z = 10.1 Black Hole in UHZ1

The recent discovery of a 4 × 107 M ⊙ black hole (BH) in UHZ1 at z = 10.3, just 450 Myr after the Big Bang, suggests that the seeds of the first quasars may have been direct-collapse BHs from the collapse of supermassive primordial stars at z ∼ 20. This object was identified in James Webb Space Telescope NIRcam and Chandra X-ray data, but recent studies suggest that radio emission from such a BH should also be visible to the Square Kilometer Array (SKA) and the next-generation Very Large Array (ngVLA). Here, we present estimates of radio flux densities for UHZ1 from 0.1 to 10 GHz, and find that SKA and ngVLA could detect it with integration times of 10–100 hr and just 1–10 hr, respectively. It may be possible to see this object with VLA now with longer integration times. The detection of radio emission from UHZ1 would be a first test of exciting new synergies between near-infrared and radio observatories that could open the era of z ∼ 5–15 quasar astronomy in the coming decade.

Octofitter: Fast, Flexible, and Accurate Orbit Modeling to Detect Exoplanets

As next-generation imaging instruments and interferometers search for planets closer to their stars, they must contend with increasing orbital motion and longer integration times. These compounding effects make it difficult to detect faint planets but also present an opportunity. Increased orbital motion makes it possible to move the search for planets into the orbital domain, where direct images can be freely combined with the radial velocity and proper motion anomaly, even without a confirmed detection in any single epoch. In this paper, we present a fast and differentiable multimethod orbit-modeling and planet detection code called Octofitter. This code is designed to be highly modular and allows users to easily adjust priors, change parameterizations, and specify arbitrary function relations between the parameters of one or more planets. Octofitter further supplies tools for examining model outputs including prior and posterior predictive checks and simulation-based calibration. We demonstrate the capabilities of Octofitter on real and simulated data from different instruments and methods, including HD 91312, simulated JWST/NIRISS aperture masking interferometry observations, radial velocity curves, and grids of images from the Gemini Planet Imager. We show that Octofitter can reliably recover faint planets in long sequences of images with arbitrary orbital motion. This publicly available tool will enable the broad application of multiepoch and multimethod exoplanet detection, which could improve how future targeted ground- and space-based surveys are performed. Finally, its rapid convergence makes it a useful addition to the existing ecosystem of tools for modeling the orbits of directly imaged planets.

Faraday detector uranium isotope ratio measurement: Insights from solution- and laser ablation-based sampling methodologies on the Neoma MC-ICP-MS

In this study we utilize an all-faraday cup detector configuration on the Neoma MC-ICP-MS to perform uranium isotope ratio determinations from certified reference materials and a nuclear fuel precursor material via solution and laser ablation based sampling methodologies. The goal in performing these measurements is primarily to demonstrate that the all-faraday cup method can produce highly precise and accurate isotope ratios even at relatively low signal intensity levels while also developing a preliminary understanding of how the complex interplay between different amplifier resistor levels (e.g. 1011 vs 1013 Ω) and integration times impacts the precision and accuracy of different types of measurements. Our results show that the faraday cups with 1013 Ω resistors in their amplifier feedback loops can be used to produce accurate and relatively precise isotope ratios for ion beams down to ∼5 K cps. However, at the lower end of the signal intensities observed in this study, longer integration times are necessary to mitigate the impact of ion beam instability that can occur during laser ablation based sampling. Despite this potential limitation, the all-faraday cup method is highly versatile as exemplified by the analysis of a collection of uranium reference materials with highly variable uranium isotopic compositions.

Non-contact quartz-enhanced photoacoustic spectroscopy

Non-contact quartz-enhanced photoacoustic spectroscopy (NC-QEPAS) was proposed and developed for trace gas analysis. The NC-QEPAS aims at solving the problem that the quartz tuning fork (QTF) must be immersed in the gases for photoacoustic wave transducing, which limits its application for corrosive and dusty gas sensing. In this work, the QTF was isolated from the gas, realizing “non-contact” detection. An elastic parylene film was synthesized and then patched to the slit of a QEPAS gas cell. With an optimized coupling effect, the parylene film shows a resonance enhancement with the QTF and acoustic micro-resonator, realizing non-contact photoacoustic detection of gas. The NC-QEPAS not only increases the photoacoustic signal amplitude but also decreases the background noise. Compared to traditional contact QEPAS with QTF immersed in the gas, the NC-QEPAS shows a signal-to-noise enhancement factor of 13. A normalized noise equivalent absorption coefficient of 8.8 × 10−9 cm−1 W Hz−1/2 was achieved. Allan deviation shows good long-term stability of the NC-QEPAS sensor. With an integration time of 1000 s, the developed QEPAS sensor shows a detection limit of 0.4 ppm. The detection limit can be further improved with longer integration time.

Conversion of 15-Minutes to 1-Minute Rainfall Distribution Derived from Tropical Rainfall Distribution Measurement

The radiocommunication sector of the International Telecommunication Union (ITU R) necessitates a 1-min integration time of rainfall rate to predict attenuation at terrestrial links and earth-space links. Since time series of rainfall that satisfies this requirement is not common, the conversion into corresponding 1-min distribution is suggested as an alternative of time series with longer integration time, T (e.g., 10-,30-,60-minutes). This research reviews existing methods for the conversion of cumulative distributions of rainfall and compares the said conversion methods. Several approaches are utilized to convert the 15-minutes rainfall rate to a 1-min rainfall rate in the tropical area of Kampung Paya Jaras. It found that Segal’s method performs the best conversion procedure overall.

Dual-elemental analysis of single particles using quadrupole-based inductively coupled plasma-mass spectrometry

Single-particle inductively coupled plasma-mass spectrometry (SP-ICP-MS) is used for elemental analysis of single particles and biological cells. Time-of-flight (TOF) mass analyzers are widely used for multiple element analysis of individual particles. Owing to the sequential nature of the mass analyzer, quadrupole-based ICP-MS generally gives poor analytical performance when more than one element are being monitored. In this study, we present the first accurate and precise dual-mass measurement of individual particles using quadrupole-based ICP-MS, with the assistance of oxygen collision gas. Simultaneous measurement of the intensity of 107Ag and 109Ag of Ag nanoparticles (AgNP) showed particle recovery of 100% and Pearson correlation coefficient of 0.97, indicating proper sampling of all particles in the ICP. This technique gives good measurement precision (RSD <8%) and high accuracy in size measurement (error <3%). This technique was further applied to determine the elemental content and isotope ratios of particles and to study cell viability after Cisplatin staining. The results are comparable to that of existing TOF and multi-collector ICP-MS, indicating that quadrupole-based ICP-MS can be a cost-effective alternative for simultaneous measurement of two isotopes. Acquisition with longer integration time and shorter settling time is also proposed to further improve the sensitivity and number of isotopes monitored. This study will potentially open up more possibilities of using quadrupole based ICP-MS in biomedical research as quantification of multi-elements in single cells is far more informative. Other possible applications include classification of cancer subtypes according to the abundance of several biomarkers, as well as elemental bio-imaging of transcripts and proteins in tissues by laser ablation.

Optimized analysis for sensitive detection and analysis of single proteins via interferometric scattering microscopy

It has been shown that interferometric detection of Rayleigh scattering (iSCAT) can reach an exquisite sensitivity for label-free detection of nano-matter, down to single proteins. The sensitivity of iSCAT detection is intrinsically limited by shot noise, which can be indefinitely improved by employing higher illumination power or longer integration times. In practice, however, a large speckle-like background and technical issues in the experimental setup limit the attainable signal-to-noise ratio. Strategies and algorithms in data analysis are, thus, crucial for extracting quantitative results from weak signals, e.g. regarding the mass (size) of the detected nano-objects or their positions. In this article, we elaborate on some algorithms for processing iSCAT data and identify some key technical as well as conceptual issues that have to be considered when recording and interpreting the data. The discussed methods and analyses are made available in the extensive python-based platform, PiSCAT 6 6 https://piscat.readthedocs.io/..

Laboratory Demonstration of the Local Oscillator Concept for the Event Horizon Imager

Black hole imaging challenges the third-generation space VLBI, the Very Long Baseline Interferometry, to operate on a 500[Formula: see text]GHz band. The coherent integration time needed here is 450[Formula: see text]s though the available space oscillators cannot offer more than 10[Formula: see text]s. Self-calibration methods might solve this issue in an interferometer formed by three antenna/satellite systems, but the need for the third satellite increases the mission costs. A frequency transfer is of special interest to alleviate both performance and cost issues. A concept of two-way optical frequency transfer is examined to investigate its suitability to enable space-to-space interferometry, in particular, to image the “shadows” of black holes from space. The concept, promising on paper, has been demonstrated by tests. The laboratory test set-up is presented and the verification of the temporal stability using standard analysis tool as TimePod has been passed. The resulting Allan Deviation is dominated by the 1/[Formula: see text] phase noise trend since the frequency transfer timescale of interest is shorter than 0.2[Formula: see text]s. This trend continues into longer integration times, as proven by the longest tests spanning over a few hours. The Allan Deviation between derived 103.2[Formula: see text]GHz oscillators is [Formula: see text]/[Formula: see text] within 10[Formula: see text][Formula: see text][Formula: see text]s that degrades twice towards the longest delay of 0.2[Formula: see text]s. The worst case satisfies the requirement with a margin of 11 times. The obtained coherence in the range of 0.997[Formula: see text]0.9998 is beneficial for space VLBI at 557[Formula: see text]GHz. The result is of special interest to future science missions for black hole imaging from space.

Born extra-eccentric: A broad spectrum of primordial configurations of the gas giants that match their present-day orbits

In a recent paper we proposed that the giant planets’ primordial orbits may have been eccentric (eJ∼eS∼ 0.05), and used a suite of dynamical simulations to show outcomes of the giant planet instability that are consistent with their present-day orbits. In this follow-up investigation, we present more comprehensive simulations incorporating superior particle resolution, longer integration times, and eliminating our prior means of artificially forcing instabilities to occur at specified times by shifting a planets’ position in its orbit. While we find that the residual phase of planetary migration only minimally alters the planets’ ultimate eccentricities, our work uncovers several intriguing outcomes in realizations where Jupiter and Saturn are born with extremely large eccentricities (eJ≃ 0.10; eS≃ 0.25). In successful simulations, the planets’ orbits damp through interactions with the planetesimal disk prior to the instability, thus loosely replicating the initial conditions considered in our previous work. Our results therefore suggest an even wider range of plausible evolutionary pathways are capable of replicating Jupiter and Saturn’s modern orbital architecture.

Impact of vertical water particle motions on focused SAR altimetry

Abstract New in this work is a new analytical derivation of a Delay-Doppler map model for Fully-Focused SAR, which includes the vertical wave particle motion and a more general surface representation. It was indeed already noticed in Egido and Smith (2017) that the open ocean surfaces decorrelate within the integration time interval, which is used in the FF-SAR processing to form the synthetic antenna. However, this was not further discussed. The impact of surface motion is expected to be larger on FF-SAR than for unfocused SAR, since a longer integration time is used in the first processing. We introduce vertical wave particle velocities and accelerations as random variables in the analytical formulation, and relate this variables to ocean-wave spectral parameters, such as the mean zero up-crossing and crest period. Further on, we show and discuss for the first time that the flat sea surface response and the probability density function of the height of scattering surface elements are not the same as in unfocused SAR. Moreover, the response of a point target differs significantly and depends on the location of a scattering surface element, the satellite orbit parameters and the tracking range. This work provides the analytical expressions and a thorough discussion of these issues, including numerical results using CryoSat-2 mission parameters.

Zwicky Transient Facility Constraints on the Optical Emission from the Nearby Repeating FRB 180916.J0158+65

Abstract The discovery rate of fast radio bursts (FRBs) is increasing dramatically thanks to new radio facilities. Meanwhile, wide-field instruments such as the 47 deg2 Zwicky Transient Facility (ZTF) survey the optical sky to study transient and variable sources. We present serendipitous ZTF observations of the Canadian Hydrogen Intensity Mapping Experiment (CHIME) repeating source FRB 180916.J0158+65 that was localized to a spiral galaxy 149 Mpc away and is the first FRB suggesting periodic modulation in its activity. While 147 ZTF exposures corresponded to expected high-activity periods of this FRB, no single ZTF exposure was at the same time as a CHIME detection. No &gt;3σ optical source was found at the FRB location in 683 ZTF exposures, totaling 5.69 hr of integration time. We combined ZTF upper limits and expected repetitions from FRB 180916.J0158+65 in a statistical framework using a Weibull distribution, agnostic of periodic modulation priors. The analysis yielded a constraint on the ratio between the optical and radio fluences of η ≲ 200, corresponding to an optical energy E opt ≲ 3 × 1046 erg for a fiducial 10 Jy ms FRB (90% confidence). A deeper (but less statistically robust) constraint of η ≲ 3 can be placed assuming a rate of and 1.2 ± 1.1 FRB occurring during exposures taken in high-activity windows. The constraint can be improved with shorter per-image exposures and longer integration time, or observing FRBs at higher Galactic latitudes. This work demonstrated how current surveys can statistically constrain multiwavelength counterparts to FRBs even without deliberately scheduled simultaneous radio observation.

GPS III Vespucci: Results of half a year in orbit

The spacecraft nicknamed Vespucci is the first GPS III satellite launched in December 2018. Numerous receivers of the global International GNSS Service network tracked the signals of this new generation of GPS spacecraft from January to July 2019. This data set serves as the basis for analysis of broadcast ephemeris performance and clock stability, as well as solar radiation pressure and satellite antenna phase center models. Different empirical orbit models are tested, and box-wing models are developed based on approximate dimensions, mass, and assumed optical properties. The box-wing models show in general a better performance than the empirical models. Compared to Block IIF satellites, the stability of the GPS III rubidium clock is higher for integration times up to 10 s. At longer integration times, the stability of both clocks is similar but the GPS III clock does not suffer from frequency-specific line bias variations that affect the apparent IIF clock. Estimated antenna phase center offsets agree on the centimeter level with the calibrations published by the manufacturer. Measurements with a 30-m high-gain antenna revealed that the satellite did not stop signal transmission in July 2019 but switched to non-standard codes and codes beyond the tracking capabilities of commercial GNSS receivers. Prior to this hibernation mode, a 70 days test without broadcast ephemeris update was conducted during which the user range error increased to roughly 1 km.

Extremely Long Convergence Times in a 3D GCM Simulation of the Sub-Neptune Gliese 1214b

Abstract We present gray gas general circulation model (GCM) simulations of the tidally locked mini-Neptune GJ 1214b. On timescales of 1000–10,000 Earth days, our results are comparable to previous studies of the same planet, in the sense that they all exhibit two off-equatorial eastward jets. Over much longer integration times (50,000–250,000 Earth days) we find a significantly different circulation and observational features. The zonal-mean flow transitions from two off-equatorial jets to a single wide equatorial jet that has higher velocity and extends deeper. The hot spot location also shifts eastward over the integration time. Our results imply a convergence time far longer than the typical integration time used in previous studies. We demonstrate that this long convergence time is related to the long radiative timescale of the deep atmosphere and can be understood through a series of simple arguments. Our results indicate that particular attention must be paid to model convergence time in exoplanet GCM simulations, and that other results on the circulation of tidally locked exoplanets with thick atmospheres may need to be revisited.

Rain attenuation distribution for satellite microwave links application in Tanzania

&lt;table width="741" border="1" cellspacing="0" cellpadding="0"&gt;&lt;tbody&gt;&lt;tr&gt;&lt;td valign="top" width="484"&gt;&lt;p&gt;Rain rate and Rain Attenuation predictions are important in radio system operating at Ku and Ka bands as they affect telecommunication systems performance. To adequately estimate rain-induced attenuation and fading, the International Telecommunication Union (ITU) recommends use of rainfall data collected using 1-minute integration time. For Tanzania, no rainfall data with 1-minute integration time is available either through measurements or conversion from rainfall data with longer integration time. In this paper the rain attenuation is predicted for seven locations in the coastal area of Tanzania. The 1- minute rainfall rate is determined by Chebil’s model using long-term measurements from Tanzania Metrological Agency (TMA) collected for a period of forty years, results obtained are used to estimate rain attenuations. By using the International Telecommunication Union-Recommendation (ITU-R) model, rain attenuation is predicted at horizontal polarization at Ku and Ka band. The results show that Unguja has the highest average annual rainfall accumulation with rain attenuation as high as ~53.22dB for Ka band and ~15.14dB for Ku band making the difference of about 38.08 between the two frequency bands. On the other hand, Kibaha which has the lowest average annual rainfall accumulation along the coast has rain attenuation of ~47.27dB for Ka and ~13.41dB for Ku bands, making the difference of 33.86dB between the frequency bands. Results obtained from this study can be useful in designing earth-satellite microwave links in the coastal area of Tanzania.&lt;/p&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/tbody&gt;&lt;/table&gt;

Optimization of a phase-space beam position and size monitor for low-emittance light sources.

The recently developed vertical phase-space beam position and size monitor (ps-BPM) system has proven to be able to measure the electron-source position, angle, size and divergence simultaneously in the vertical plane at a single location of a beamline. The optimization of the ps-BPM system is performed by ray-tracing simulation to maximize the instrument sensitivity and resolution. The contribution of each element is studied, including the monochromator, the K-edge filter, the detector and the source-to-detector distance. An optimized system is proposed for diffraction-limited storage rings, such as the Advanced Photon Source Upgrade project. The simulation results show that the ps-BPM system can precisely monitor the source position and angle at high speed. Precise measurements of the source size and divergence will require adequate resolution with relatively longer integration time.

Forecast Sensitivity Observation Impact in the 4DVAR and Hybrid-4DVAR Data Assimilation Systems

AbstractIn this study, the observation impacts on 24-h forecast error reduction (FER), based on the adjoint method in the four-dimensional variational (4DVAR) data assimilation (DA) and hybrid-4DVAR DA systems coupled with the Unified Model, were evaluated from 0000 UTC 5 August to 1800 UTC 26 August 2014. The nonlinear FER in hybrid-4DVAR was 12.2% greater than that in 4DVAR due to the use of flow-dependent background error covariance (BEC), which was a weighted combination of the static BEC and the ensemble BEC based on ensemble forecasts. In hybrid-4DVAR, the observation impacts (i.e., the approximated nonlinear FER) for most observation types increase compared to those in 4DVAR. The increased observation impact from using hybrid-4DVAR instead of 4DVAR changes depending on the analysis time and regions. To calculate the ensemble BEC in hybrid-4DVAR, analyses at 0600 and 1800 UTC (0000 and 1200 UTC) used 3-h (9-h) ensemble forecasts. Greater observation impact was obtained when 3-h ensemble forecasts were used for the ensemble BEC at 0600 and 1800 UTC, than with 9-h ensemble forecasts at 0000 and 1200 UTC. Different from other observations, the atmospheric motion vectors (AMVs) deduced from geostationary satellite are more frequently observed in the same area. When the ensemble forecasts with longer integration times were used for the ensemble BEC in hybrid-4DVAR, the observation impact of the AMVs decreased the most in East Asia. This implies that the observation impact of AMVs in East Asia shows the highest sensitivity to the integration time of the ensemble members used for deducing the flow-dependent BEC in hybrid-4DVAR.

Receiver array design for sonothrombolysis treatment monitoring in deep vein thrombosis

High intensity focused ultrasound (HIFU) can disintegrate blood clots through the generation and stimulation of bubble clouds within thrombi. This work examined the design of a device to image bubble clouds for monitoring cavitation-based HIFU treatments of deep vein thrombosis (DVT). Acoustic propagation simulations were carried out on multi-layered models of the human thigh using two patient data sets from the Visible Human Project. The design considerations included the number of receivers (32, 64, 128, 256, and 512), their spatial positioning, and the effective angular array aperture (100° and 180° about geometric focus). Imaging array performance was evaluated for source frequencies of 250, 750, and 1500 kHz. Receiver sizes were fixed relative to the wavelength (pistons, diameter = λ/2) and noise was added at levels that scaled with receiver area. With a 100° angular aperture the long axis size of the −3 dB main lobe was ~1.2λ—i.e. on the order of the vessel diameter at 250 kHz (~7 mm). Increasing the array aperture to span 180° about the geometric focus reduced the long axis by a factor of ~2. The smaller main lobe sizes achieved by imaging at higher frequencies came at the cost of increased levels of sensitivity to phase aberrations induced during acoustic propagation through the intervening soft tissue layers. With noise added to receiver signals, images could be reconstructed with peak sidelobe ratios < −3 dB using single-cycle integration times for source frequencies of 250 and 750 kHz (NRx ⩾ 128). At 1500 kHz, longer integration times and/or higher element counts were required to achieve similar peak sidelobe ratios. Our results suggest that a modest number of receivers(i.e. NRx = 128) arranged on a semi-cylindrical shell may be sufficient to enable passive acoustic imaging with single-cycle integration times (i.e. volumetric rates up to 0.75 MHz) for monitoring cavitation-based HIFU treatments of DVT.

Modulation transfer spectroscopy based on acousto-optic modulator with zero frequency shift**Project supported by the National Key Research and Development Program of China (Grant No. 2016YFA0302101), the Foundation of China Academy of Space Technology, and the Initiative Program of State Key Laboratory of Precision Measurement Technology and Instruments, China.

We present a modulation transfer spectroscopy (MTS) configuration based on an acousto-optic modulator by using a variant of the typical double pass structure. One beam is modulated by using an acousto-optic modulator in opposite diffraction order to cancel the carrier frequency shift and produce a modulated pump beam. The line shape performance is investigated theoretically and experimentally. Laser frequency stabilization of the proposed configuration is demonstrated for the 133Cs |62S1/2, F = 4⟩ → |62P3/2, F′ = 5⟩ transition. The Allan deviations, which are measured by using beat note signals and the three-cornered hat method, are 3.6 × 10−11 in an integration time of 100 s and approximately 4 × 10−11 in a longer integration time.